Radial piston pump for fuel injection system having improved high-pressure resistance

ABSTRACT

A radial piston pump has a pump housing containing pump elements and whose high-pressure conduits extending in the pump housing are embodied so as to significantly increase the permissible operating pressures.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 35 USC 371 application of PCT/DE 03/01541 filed onMay 13, 2003.

BACKGROUND OF THE INVENTION

1. Field Of The Invention

2. Description of the Prior Art

The invention relates to a radial piston pump for high-pressure fueldelivery in fuel injection systems of internal combustion engines,particularly in a common rail injection system, preferably with a numberof pump elements arranged radially in relation to a drive shaftsupported in a pump housing, the pump elements being actuated by thedrive shaft and each having a respective inlet side and high-pressureside, and with high-pressure conduits in the pump housing, each of whichconnects the high-pressure side of a respective pump element to ahigh-pressure connection in the pump housing.

A radial piston pump of the type with which this invention is concernedis known, for example, from DE 197 29 788.9 A1. This mass-producedradial piston pump achieves operating pressures of up to 1300 bar on thehigh-pressure side. These pressures result in considerable mechanicalstresses in the pump housing.

In order to further improve the emissions behavior of internalcombustion engines and to further increase efficiency, it is necessaryto provide higher injection pressures than the above-mentioned 1300 bar.

The object of the invention is therefore to modify a radial piston pumpso that it can be used for pressures of up to 2000 bar.

In a radial piston pump for high-pressure fuel delivery in fuelinjection systems of internal combustion engines, preferably with anumber of pump elements arranged radially in relation to a drive shaftsupported in a pump housing, the pump elements being actuated by thedrive shaft and each having a respective inlet side and high-pressureside, and with high-pressure conduits in the pump housing, each of whichconnects the high-pressure side of a respective pump element to ahigh-pressure connection in the pump housing, this object is attainedaccording to the invention in that the high-pressure conduits have asfew junctions as possible and in that the angle at which onehigh-pressure conduit branches off from another high-pressure conduit isas close as possible to 90°.

SUMMARY AND ADVANTAGES OF THE INVENTION

The routing of the high-pressure conduits in the pump housing in themanner according to the invention makes it possible, in spite ofincreased pump pressures, to achieve a reduction in the maximal stressesoccurring at critical points in the pump housing. As a result, theradial piston pump according to the invention can be operated at higherpressures while at the same time experiencing a reduced strain on thematerial.

The maximal stresses occurring are determined by means of FEMcalculations. In trials with prototypes, the improved compressionstrength of the pump housing turned out to be due to the routing of thehigh-pressure conduits in the manner according to the invention.

According to a modification of the invention, the surfaces of thehigh-pressure conduits are compacted and provided with compressiveinternal stresses in particular by means of a sphere, whose diameter isslightly greater than the diameter of the high-pressure conduits, beingdrawn or pressed through the high-pressure conduits. This step furtherincreases the compression strength of the pump housing in the region ofthe high-pressure conduits.

According to the invention, it is also possible for the high-pressureconduits to be hardened, in particular induction hardened. In order tofurther minimize the maximal stresses of the pump housing that occurwith the exertion of pressure, the high-pressure conduits are rounded,in particular by means of hydrodynamic erosion, in the region of crosssectional changes and/or junctions with other high-pressure conduits.

According to a particularly advantageous embodiment of the radial pistonpump according to the invention, the high-pressure conduits arereinforced by a tubular insert, in particular an insert made of ahigh-strength material; high-tensile steel has turned out to be aparticularly suitable material. The tubular inserts according to theinvention are, like a core, inserted into the mold before casting. Thecasting bonds the pump housing and tubular inserts to each other in avery intimate fashion. Because of the tubular inserts, the high-pressureconduits are comprised of a different material, particularly preferablya stronger one, than the rest of the pump housing, and as a result, thecomponent strength is adapted to the local strains and stresses. Thisassures that, on the one hand, in the region of the high-pressureconduits where the highest stresses occur during operation, ahigher-strength material is used, which can reliably withstand thestresses that occur, and on the other hand, the rest of the pump housingcan be made of a comparatively inexpensive material that can also beeasily machined and has good antifrictional properties.

Another advantage of the tubular inserts according to the invention isthat by contrast with conventional bores, the high-pressure conduits canbe embodied as curved or partially curved. It is also possible to use aseparate insert to connect the high-pressure side of each pump elementdirectly to the high-pressure connection in the pump housing, thuseliminating the need for any junctions in the high-pressure conduits.This has a favorable effect on the maximal stresses occurring in thepump housing, on the manufacturing costs, and in particular on theproduction safety.

According to another variant of a radial piston pump according to theinvention, each pump element has a cylinder bore and a cylinder head,the piston oscillates in the piston bore and feeds a delivery chamber, afirst check valve is disposed on the inlet side, and a second checkvalve is disposed on the high-pressure side. It has turned out to beadvantageous if the cylinder bore is embodied as a blind bore and thefirst check valve is disposed at the bottom of the blind bore. Embodyingthe cylinder bore as a blind bore eliminates one seal location.

According to another modification of the invention, the second checkvalve has a sleeve with a stepped center bore, the stepped center borehas a sealing seat for a valve element, in particular a ball,particularly preferably a ceramic ball, and the sleeve of a screwsealing plug is pressed against the cylinder head in a sealed fashion.This second check valve has the advantage that it is very simplydesigned and can be tested outside the radial piston pump. All thatneeds to be provided inside the radial piston pump or pump element is asealing surface that seals the screwed-in second check valve at its end.In production engineering terms, a sealing surface of this kind is easyto control, thus making it easier to seal the high-pressure side of thepump element in relation to the environment at this location through theuse of the second check valve according to the invention.

Sealing the high-pressure side in relation to the environment isparticularly effective if the sleeve has a biting edge on its endsurface oriented toward the screw sealing plug, thus increasing thesurface pressure and also permitting a plastic deformation of thesealing surfaces, which further improves the sealing function.

If the sleeve is pressed-fitted onto the screw sealing plug,particularly in the region of the center bore, then this furthersimplifies the installation of the check valve since it assures that theassembled, tested check valve will not come apart.

In order to assure a constant hydraulic connection between the deliverychamber on the one hand and the high-pressure connection in the pumphousing on the other when the second check valve is open, the sleeve hasa lateral bore and an annular groove, and the lateral bore and annulargroove produce a hydraulic connection between the center bore and thedelivery chamber.

In another variant of a first or second check valve, a sealing seat isincorporated into the side of the cylinder head oriented toward the pumphousing; the check valve has a cage, which contains a closing springthat acts on the valve member, in particular a ball. The closing springreduces the return flow of fuel, which has an advantageous effect on thepump efficiency.

The installation of the check valve according to the invention into thepump element is simplified if the cage is press-fitted into a steppedbore encompassing the sealing seat.

In an embodiment that is advantageous from a production engineeringstandpoint, the cylinder bore is embodied as a blind bore and the firstcheck valve is disposed at the bottom of the blind bore so that thesealing seat of the first and second check valves can be produced in onesetup and the first and second check valves are installed in the samedirection.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages and advantageous features of the invention with beapparent from the description contained herein below, taken inconjunction with the drawings, in which:

FIG. 1 a is a front view of a first exemplary embodiment of a radialpiston pump according to the invention.

FIG. 1 b is a longitudinal section through the exemplary embodimentaccording to FIG. 1 a,

FIG. 1 c is a cross section through the exemplary embodiment, along theline A-A of FIG. 1 b,

FIG. 2 a is a cross section through the first exemplary embodiment,along the line B-B of FIG. 1 b,

FIG. 2 b is an embodiment alternative to the one in FIG. 2 a,

FIG. 3 is a three-dimensional depiction of another exemplary embodimentof a pump housing according to the invention,

FIG. 4 shows another exemplary embodiment of a cylinder head accordingto the invention,

FIGS. 5 and 6 are longitudinal sections through other exemplaryembodiments of cylinder heads according to the invention, and

FIGS. 7 a and b show details of the check valve according to theexemplary embodiment in FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows an exemplary embodiment of a radial piston pump accordingto the invention in a view from the front (FIG. 1 a), in a longitudinalsection (FIG. 1 b), and in a cross section along the section line A-A.The radial piston pump is comprised of a pump housing 1 in which a driveshaft 3 is mounted in rotary fashion. The pump housing 1 can beadvantageously made of cast iron with globular graphite (GGG). The driveshaft 3 has an eccentric section 5. By means of a polygon ring 7, theeccentric section 5 drives three pump elements 9 distributed over thecircumference. Each pump element 9 has a piston 11 that is guided in acylinder bore 13 and delimits a delivery chamber 15. Not all of theindividual components of all of the pump elements 9 in FIG. 1 c areprovided with reference numerals in order to avoid unnecessarilycompromising clarity. The three pump elements 9, however, are allembodied identically.

A cylinder head 17 of the pump elements 9 contains an inlet side 19 anda high-pressure side 21. The inlet side 19 of the cylinder head 17 issupplied with fuel via a low-pressure bore 23 in the pump housing. Onthe inlet side 19, a first check valve 25 is provided, which preventsthe return flow of fuel (not shown) from the delivery chamber 15 intothe low-pressure bore 23.

The high-pressure side 21 of the pump element 9 feeds into ahigh-pressure conduit 27 in the pump housing 1. On the high-pressureside 21 of the pump element, a second check valve 29 is provided, whichprevents the return flow of highly pressurized fuel from thehigh-pressure conduit 27 into the delivery chamber 15. The pump elements9 are screw-mounted to the pump housing 1 by means of screws, not shown,and are pressed against a cylinder base surface 31 of the pump housing 1by this screw connection.

Each pump element 9 has a high-pressure conduit 27 leading from it inthe pump housing 1, which feeds into a high-pressure connection notshown in FIGS. 1 a to 1 c. The course of the high-pressure conduits willbe explained below in conjunction with FIGS. 2 and 3. The lower half ofa second high-pressure conduit 27 is depicted in FIG. 1 b. Since thishigh-pressure conduit extends essentially perpendicular to the plane ofthe drawing, it is depicted as a circular area in FIG. 1 b.

The above-described design and the function of such a radial piston pumpare known from the prior art, for example from DE 197 29 788.9 A1, thedisclosure of which is expressly incorporated herein by reference, thusrendering a detailed explanation of the function unnecessary inconnection with the current invention.

FIG. 2 shows a cross section through a pump housing 1 along the sectionline B-B. This depiction clearly shows the course of the high-pressureconduits 27 according to a first exemplary embodiment of the invention.

FIG. 2 shows only the pump housing 1. The pump elements 9 are not shownin FIG. 2. Since the high-pressure conduits 27 in the pump housing 1 aresubjected to the full delivery pressure of the pump elements,considerable stresses are produced in the pump housing 1 during theoperation of the radial piston pump, which are substantially due to thepressures prevailing in the high-pressure conduits 27 a to 27 c. Up tothis point, mass-produced radial piston pumps with inserted pumpelements 9 have been used at operating pressures of up to 1300 bar. Ifit is now necessary to further increase the operating pressures, then itis necessary to maintain or even improve the fatigue strength of thepump housing, primarily in the region of the high-pressure conduits 27a. Arranging the high-pressure conduits 27 a, 27 b, and 27 c in themanner according to the invention makes it possible, in the presence ofthe same pressures, to drastically reduce the stresses occurring in thepump housing so that the permissible operating pressures can beincreased to over 1800 bar with the same component strength. Even atthese operating pressures, which have been increased in comparison tothe above-mentioned operating pressures according to the prior art(maximally 1300 bar), the mechanical strain on the pump housing is lowerthan in the radial piston pumps according to the prior art.

This is achieved according to the invention by minimizing the number ofhigh-pressure conduits. In the current instance, three high-pressureconduits 27 a, 27 b, 27 csuffice to produce a hydraulic connection fromthe three cylinder base surfaces 31 to a high-pressure connection 33.The high-pressure conduit 27 b here branches off from the high-pressureconduit 27 a at an angle α of approximately 90° . The angle α should beas close as possible to 90° in order to minimize the stresses occurringat the first junction 35 during operation. The high-pressure conduit 27aintersects the high-pressure conduit 27 cat an angle β and forms asecond junction 37. As shown in FIGS. 2 a and 2 b , the high pressureconduits (27) extend to the three surfaces (31) where they connect tothe three pump elements and they have fewer junctions (35,37) than thenumber of pump elements. The angle β should also be as close as possibleto 90° , however, it is not always possible to make angles α and β afull 90° , given the structural conditions in the pump housing 1, soinstead they are characterized as substantially 90° . FEM calculationshave demonstrated that arranging the high pressure conduits 27 a , 27 b,and 27 c in the manner according to the invention has resulted in areduced maximal stress in the pump housing 1 compared to mass producedradial piston pumps, even at Significantly higher operating pressures.This has made it possible to increase the permissible operatingpressures from 1300 bar to over 1800 bar, without being forced to selecta material that is more expensive than the cast iron with globulargraphite (GGG) known from prior art.

A further increase in engineering strength can be achieved byreinforcing the high-pressure conduits 27 a with tubular inserts, inparticular ones made of a high-strength material. FIG. 2 b shows anexemplary embodiment of a pump housing 1 in which the high-pressureconduits 27 a to 27 c have been reinforced with tubular inserts. Thetubular inserts 39 are attached to one another in the region of thefirst junction 35 and the second junction 37. They are advantageouslyattached to one another by means of welding or soldering. These tubularinserts 39 a 31 a to 39 c can further increase the strength of the pumphousing 1. The tubular inserts 39 a to 39 c are inserted into the moldbefore the casting of the pump housing 1. During the subsequent castingof the pump housing 1, the tubular inserts 39 are intimately bonded tothe pump housing 1, thus resulting in an optimal transmission of forcebetween the tubular insert 39 and the pump housing 1.

FIG. 3 is a three-dimensional depiction of another exemplary embodimentof a pump housing according to the invention. It is clear that in thisexemplary embodiment, the high-pressure conduits 27 a, 27 b, and 27 care embodied as curved and each lead directly, i.e. without junctions,from a cylinder base surface 31 to the high-pressure connection 33. Inthis embodiment, the strains in the pump housing 1 resulting fromoperating pressures are further reduced due to the lack of junctions.From a production engineering standpoint, this embodiment can beproduced by means of curved tubular inserts 39 a, 39 b, and 39 c.

FIG. 4 shows an exemplary embodiment of a radial piston pump accordingto the invention in which the cylinder bore 13 in the pump element 9 isembodied as a blind bore. At the bottom of the blind bore, a sealingseat 41 is provided for the first check valve 25. The first check valve25 can be embodied as structurally identical to the second check valve29 described in conjunction with FIGS. 6 and 7. In the exemplaryembodiment according to FIG. 4, the piston 11 is likewise driven bymeans of a polygon ring and a piston base plate 43. The invention,however, is not limited to radial piston pumps with pump elements 9driven in this manner. On the contrary, it can also include alternativedrive methods such as disk cams or the like. The piston bases can alsoinclude tappets (not shown) that are guided in the pump housing 1.

FIG. 5 a shows a cross section through a cylinder head 17 of anotherexemplary embodiment of a radial piston pump according to the invention.The first check valve 25 corresponds to the check valve 25 shown inFIG. 1. The second check valve 29 indicated in FIG. 1 b will beillustrated and explained below in conjunction with FIG. 5 a and FIG. 5b, which shows an enlarged detail from FIG. 5 a.

The second check valve 29 is comprised of a sleeve 45. A sealing seat 49for a ball 51, in particular a ceramic ball, is let into the steppedbore 47 of sleeve 45. A closing spring 53, which is supported against ascrew sealing plug 55, presses the ball 51 against the sealing seat 49.The use of a closing spring 53 can increase the efficiency of the radialpiston pump according to the invention by several percentage pointssince this prevents a return flow of fuel from the high-pressure conduit27 not shown in FIG. 5 b into the delivery chamber 15, also now shown.The sleeve 45 is press-fitted onto a shoulder 57 of the screw sealingplug 55 so that the second check valve 29 according to the invention canbe preassembled with the screw sealing plug 55 and tested ahead of time.On its end surface 59 oriented away from the screw sealing plug 55, thesleeve 45 has a circumferential biting edge 61, which is used to sealthe second check valve 29 against the cylinder head 17. A lateral bore63 and an annular groove 64 in the sleeve 45 permit fuel to flow outinto a bore 65 in the cylinder head 17 when the second check valve isopen.

FIG. 6 shows another exemplary embodiment of a radial piston pumpaccording to the invention. In this exemplary embodiment, the secondcheck valve 29 is disposed on the side 67 of the cylinder head 17oriented into the housing 1.

The sealing seat 49 is incorporated into the cylinder head 17. Thesealing seat 49 is adjoined by a cylindrical bore 68. The bore 68 has acage 69 press-fitted into it, which contains a closing spring 53 thatpresses the ball 51 against the sealing seat 49. This second check valve29 according to the invention is very easy to manufacture and assemble.It can also be used as a first check valve 25, for example in anembodiment according to FIG. 4. In this instance, it is veryadvantageous in terms of production that the sealing seat 41 of thefirst check valve 25 and the sealing seat 49 of the second check valveare disposed parallel to each other, which makes it easier to machinethem in one setup of the cylinder head.

FIG. 7 a shows a longitudinal section through the cage 69 with theclosing spring 53 inserted and FIG. 7 b shows a top view of the cage 69without the closing spring 53.

All features mentioned or depicted in the drawings, their description,and the claims can be essential to the invention both individually andin arbitrary combinations with one another.

The foregoing relates to preferred exemplary embodiments of theinvention, it being understood that other variants and embodimentsthereof are possible within the spirit and scope of the invention, thelatter being defined by the appended claims.

1. In a radial piston pump for high-pressure fuel delivery in fuel injection systems of internal combustion engine, including a number of pump elements (9) arranged radially in relation to a drive shaft (3) supported in a pump housing (1), the pump elements (9) being actuated by the drive shaft (3) and each having a respective inlet side (19) and high-pressure side (21), and with high-pressure conduits (27) in the pump housing (1), each of which connects the high-pressure side (21) of at least one pump element (9) to a high-pressure connection (33) in the pump housing (1), the improvement comprising a first one of the high-pressure conduits (27) which connects directly to two pump elements, and a second of the high-pressure conduits which connects directly to connecting another pump element and also connects directly to said first high-pressure conduit at a junction which has an angle (α, β) which is substantially 90°, and wherein the high-pressure connection (33) connects directly to only one of said first or second high-pressure conduits, and does so at an angle (α, β) which is also substantially 90°.
 2. In a radial piston pump for high-pressure fuel delivery in fuel injection systems of internal combustion engine, including a number of pump elements (9) arranged radially in relation to a drive shaft (3) supported in a pump housing (1), the pump elements (9) being actuated by the drive shaft (3) and each having a respective inlet side (19) and high-pressure side (21), and with high-pressure conduits (27) in the pump housing (1), each of which connects directly to the high-pressure side (21) of a respective pump element and one of which directly connects (9) to a high-pressure connection (33) in the pump housing (1), the improvement comprising the high-pressure conduits (27) having fewer junctions (35, 37) then the number of pump elements and the angle (α, β) at which one high-pressure conduit (27 a, 27 b, 27 c) branches off from another high-pressure conduit (27 a, 27 b, 27 c) is substantially 90°, wherein the entire inner surfaces of the high pressure conduits (27 a, 27 b, 27 c) are compacted.
 3. The radial piston pump according to claim 1, wherein a sphere whose diameter is slightly larger than the diameter of the high pressure conduits (27 a, 27 b, 27 c) is drawn or pressed through the entire length of the high pressure conduits (27 a, 27 b, 27 c) to compact the surfaces.
 4. The radial piston pump according to claim 1, wherein the high pressure conduits (27 a, 27 b, 27 c) are hardened by induction hardening.
 5. The radial piston pump according to claim 1, wherein the high pressure conduits are rounded by means of hydrodynamic erosion, in the region of cross sectional changes and/or junctions (35, 37) with other high pressure conduits.
 6. In a radial piston pump for high-pressure fuel delivery in fuel injection systems of internal combustion engine, including a number of pump elements (9) arranged radially in relation to a drive shaft (3) supported in a pump housing (1), the pump elements (9) being actuated by the drive shaft (3) and each having a respective inlet side (19) and high-pressure side (21), and with high-pressure conduits (27) in the pump housing (1), each of which connects the high-pressure side (21) of a respective pump element (9) to a high-pressure connection (33) in the pump housing (1), the improvement comprising the high-pressure conduits (27) having fewer junctions (35, 37) then the number of pump elements and the angle (α, β) at which one high-pressure conduit (27 a, 27 b, 27 c) branches off from another high-pressure conduit (27 a, 27 b, 27 c) is substantially 90°, wherein each of the high pressure conduits (27 a, b, c) is reinforced by a tubular insert (39 a, b, c) each of which is encased within the housing.
 7. The radial piston pump according to claim 6, wherein the inserts (39 a, b, c) are comprised of a high-tensile steel.
 8. The radial piston pump according to claim 1, wherein at least one high-pressure conduit is embodied as partially curved, and each of the conduits are encased within the housing.
 9. The radial piston pump according to claim 1, wherein each pump element (9) has a piston (11), a cylinder bore (13), and a cylinder head (17), wherein the piston (11) oscillates in the cylinder bore (13) and delimits a delivery chamber (15), wherein a first check valve (25) is disposed on the inlet side (19), and wherein a second check valve (29) is disposed on the high-pressure side (21).
 10. The radial piston pump according to claim 9, wherein the second check valve (29) has a sleeve (45) with a stepped center bore (47), wherein the stepped center bore (47) has a sealing seat (49) for a valve ball (51), and wherein the sleeve (45) is pressed against the cylinder head (17) in a sealed fashion by a screw sealing plug (55).
 11. The radial piston pump according to claim 10, wherein the sleeve (45) has an end surface (59) which is oriented away from the screw sealing plug (55) and is embodied as a sealing surface with a biting edge (61).
 12. The radial piston pump according to claim 10, wherein the sleeve (45) is press-fitted onto the screw sealing plug (55) in the region of the center bore (47).
 13. The radial piston pump according to claim 10, wherein the sleeve (45) has a lateral bore (61) and an annular groove (63), and wherein the lateral bore (61) and the annular groove (63) hydraulically connect the center bore (47) to the delivery chamber (15).
 14. The radial piston pump according to claim 9, wherein each cylinder head (17) has a side (67) which is oriented toward the pump housing, and a sealing seat (49) of the second check valve (29) is disposed on the side (67) of the cylinder head (17) which is oriented toward the pump housing (1).
 15. The radial piston pump according to claim 1, wherein a first and/or a second check valve (25, 29) has a cage (69), and that the cage (69) contains a closing spring (53) that acts on a valve element (51).
 16. The radial piston pump according to claim 15, wherein the cage (59) is press-fitted into a stepped bore (65) that is embodied in the cylinder head (17) and encompasses the sealing seat (49).
 17. The radial piston pump according to claim 1, wherein a cylinder bore (13) is embodied as a blind bore and that a first check valve (25) is disposed at the bottom of the blind bore.
 18. In a radial piston pump for high-pressure fuel delivery in fuel injection systems of internal combustion engines, including a number of pump elements (9) arranged radially in relation to a drive shaft (3) supported in a pump housing (1), the pump elements (9) being actuated by the drive shaft (3) and each having a respective inlet side (19) and high-pressure side (21), and with high-pressure conduits (27) in the pump housing (1), each of which connects the high-pressure side (21) of at least one pump element (9) to a high-pressure connection (33) in the pump housing (1), the improvement comprising a first one of the high-pressure conduits (27) connecting directly to two of the pump elements, and a second of the high-pressure conduits connecting directly to a third pump element (9) and also directly to the first high-pressure conduit, wherein the angle (α, β) at which said two high-pressure conduits meet is substantially at 90°. 